Peel and finely chop the onion. Heat 1 tablespoon of oil in a saucepan. Sauté the onion in it. Peel the garlic and press it through a garlic press to the onion. Add tomatoes with juice, chop with a wooden spoon and simmer for about 15 minutes.
In the meantime, clean and trim the mushrooms. Wash basil, dab dry and pluck. Heat the remaining oil in a pan and fry the mushrooms for about 5 minutes. In the meantime add broth and about 150 g cream to the tomatoes and bring to the boil.
Stir the starch with 1 tablespoon of water until smooth and thicken the sauce with it. Season with salt, cayenne pepper and vinegar. Remove the mushrooms from the pan and add them to the tomato sauce. Cut basil into strips except for a little bit for garnishing and stir into the mushrooms.
Arrange in a bowl, garnish with the remaining basil and drizzle with the remaining cream. Baguette tastes good with it.